1. Field of the Invention
The present invention generally relates to a method of inhibiting degradation of a transistor gate oxide film due to ultraviolet rays in a High Density Plasma (hereinafter, referred to as “HDP”) process, and more specifically, to a method for effectively preventing ultraviolet rays from permeating into a gate insulating oxide film by implanting impurity into the surface of an oxide film so as to change a surface characteristic of the oxide film.
2. Description of the Prior Art
A HDP process utilizes high power plasma, which generates ultraviolet rays (UV). The UV is known to have a predetermined wavelength ranging from about 200 to 800 nm. According to the Plank's Law on wavelength of light and its energy, the energy E is proportional to frequency (E=hν; h=Plank's constant, ν=frequency of light). Since the frequency ν is inversely proportional to the wavelength of light, E becomes larger as the wavelength of light becomes shorter. Accordingly, the UV having a wavelength ranging from 200 to 800 nm has an energy ranging from about 5 eV to 1.5 eV. If such energy reaches a silicon substrate, an Electron-Hole Pair is formed. The formation of the Electron-Hole Pair is generally occurs when an energy larger than the Band-Gap energy of 1.1 eV in the silicon is injected thereto. The electron is again trapped in a gate oxide film, thereby degrading characteristics of the oxide film.
A Plasma Induced Damage (hereinafter, referred to as “PID”) or a Plasma Induced Radiation Damage (hereinafter, referred to as “PIRD”) of the HDP cannot be controlled in the conventional process. A method of inhibiting the use of HDP or reducing power of plasma to reduce the PID has been proposed. However, the method reduces the uniform deposition ability which is an advantage in using HDP, resulting in short circuits in a subsequent process.
Recently, a method of deposition an amorphous silicon film after a formation of a transistor has been proposed to inhibit degradation of a gate oxide film by PID or PIRD. In accordance with the method, a formation process of contact for connecting wires cannot be performed by a single etching process. In addition, a possibility of a short circuit between wires by the amorphous silicon film exists.